EP3215764B1 - Method for operating a motor vehicle comprising an all-wheel drive that can be enabled and disabled by determining an angular acceleration of components which are uncoupled when the all-wheel drive is disabled - Google Patents

Description

The invention relates to a method for operating a motor vehicle with an on and off switchable four-wheel drive and a drive train comprising two controlled by a controller couplings for switching on and off of the four-wheel drive and between the clutches rotating components, which are driven with switched four-wheel drive and at switched off all-wheel drive from the rest of the powertrain are disconnected.

From the DE 10 2012 020 908 A1 the applicant is already known a method of the type mentioned for operating a motor vehicle with four-wheel drive, having a permanently driven primary or front axle and an on and off secondary or rear axle whose drive from a control device in response to a current driving situation or is switched off. One of the main advantages of such a switched on and off all-wheel drive is that the fuel consumption of the motor vehicle can be minimized by the four-wheel drive is switched off when it is not needed, thereby in particular the power losses or the drag torque of the axle of the disconnectable secondary or Minimize rear axle.

The drive train of the motor vehicle according to DE 10 2012 020 908 A1 includes a so-called four-wheel clutch in the form of a clutch that is closed when switched four-wheel drive and distributed by the engine torque distributed to both axles of the motor vehicle and is open when switched off all-wheel drive and provided by the engine torque only the permanently driven primary or front axle supplies. The switchable secondary or rear axle comprises a second clutch in the form of a separating clutch, which is closed and opened together with the four-wheel clutch. Between the two clutches are several rotating components, including one of the four-wheel drive to the secondary or rear axle connecting shaft, the rotatably connected to the connecting shaft output side components of the all-wheel drive, and the axle of the secondary or rear axle together with differential compensation and their rotating components. In the closed state of the two clutches all of these rotating components are driven by the internal combustion engine. When the clutches during open the drive, this leads to the fact that said components are disconnected from the drive train and rotate freely. Since the components are decelerated by an applied drag torque, their speed gradually decreases to zero. The drag torque includes braking torque components, which result inter alia from the Ölpantschen a ring gear of the axle of the secondary or rear axle and the bearing friction of the connecting shaft in the pivot bearings, and accelerating torque components, among other things, a speed difference between the drive-side and the output-side components of the oil-filled Four-wheel clutch as well as from the friction in the differential compensation result.

At the next connection of the four-wheel drive, the previously decoupled from the drive train components must be accelerated again or brought to speed, the necessary acceleration or necessary for acceleration torque of the internal combustion engine depends on the instantaneous speed of the decoupled components and the adjacent drag torque.

For this reason, the knowledge of the applied when switched off four-wheel drive drag torque is important to adjust the speed of the decoupled and freely rotating or stopped components on the one hand as fast as possible to the speed of the other components of the powertrain when switching the secondary or rear axle on the other hand, without it on the other hand, a noticeable jerk in the drive train and thus in the motor vehicle. In other words, in order to achieve a comfort-optimal connection, the acceleration must be the slower, the greater the drag torque or the drag losses, which counteract acceleration.

The applied drag torque depends on several parameters, namely the speed of the components, the oil level in the clutches and the axle drive, the temperature of the lubricating oil in the axle drive and the inlet or wear of the bearings and seals. The oil level in the clutches and in the axle drive is known, for example, while the speed and the lubricating oil temperature can be measured. The running-in condition or wear of the bearings and seals are unknowns that need to be estimated. The applied drag torque is determined immediately for different driving conditions depending on the parameters mentioned above on a test bench and stored permanently in the control unit of the motor vehicle.

To save costs, however, sensors are increasingly being dispensed with, including a sensor for measuring the lubricating oil temperature in the axle drive of the deactivatable secondary or rear axle. However, if the unknown inlet or wear of the bearings and seals are added to other unknowns, such as the lubricating oil temperature or the oil level in the axle, a meaningful statement about the applied drag torque is hardly possible. US 2007/193793 A discloses a method according to the preamble of claim 1. Based on this, the present invention seeks to improve a method of the type mentioned in that defects and especially bearing defects of the rotating components can be detected early and that the applied drag torque without the Knowledge of the lubricating oil temperature in the axle drive can be determined.

This object is achieved by a method according to claim 1.

der Winkelgeschwindigkeit ω, der abgekoppelten Bauteile ermittelt. Die Drehzahl von einem der abgekoppelten Bauteile kann zweckmäßig mit Hilfe eines Drehzahlsensors gemessen werden, der zum Beispiel die Drehzahl der Verbindungswelle oder eines Differenzialkorbs des Ausgleichsdifferenzials ermittelt. Sofern sich die Drehzahl von anderen abgekoppelten Bauteilen von der gemessenen Drehzahl unterscheidet, kann sie über das bekannte Übersetzungsverhältnis leicht berechnet werden.
In der Regel wird es sich bei der ermittelten Winkelbeschleunigung α um eine negative Winkelbeschleunigung handeln, das heißt um eine Abbremsung. Wenn der Betrag der negativen Winkelbeschleunigung oberhalb von einem zuvor durch Prüfstandversuche ermittelten vorgegebenen Schwellenwert oder Bereich liegt, wird eines der abgekoppelten Bauteile zu stark abgebremst, wodurch frühzeitig auf einen Lagerdefekt in einem Lager von einem der abgekoppelten Bauteile geschlossen und dieses entsprechend ausgetauscht werden kann, bevor es zu einem Lagerfressen kommt. Auch eine Unterschreitung eines vorgegebenen Schwellenwerts oder Bereichs kann auf einen Defekt hindeuten.When switched off all-wheel drive, the speed of at least one of the decoupled components is measured at a time interval and from this is an angular acceleration α of the decoupled components, that is the derivative

the angular velocity ω, the decoupled components determined. The rotational speed of one of the decoupled components can be measured expediently with the aid of a rotational speed sensor which determines, for example, the rotational speed of the connecting shaft or of a differential cage of the compensating differential. If the speed of other decoupled components differs from the measured speed, it can be easily calculated over the known gear ratio.
As a rule, the determined angular acceleration α will be a negative angular acceleration, ie a deceleration. If the amount of negative angular acceleration is above a predetermined threshold or range previously determined by bench tests, one of the decoupled components is braked too strongly, allowing early detection of a bearing failure in a bearing of one of the decoupled components and replacement thereof it comes to a camp eater. Falling below a given threshold or range may also indicate a defect.

In addition, the applied drag torque is calculated from the determined angular acceleration α, since this is the product of the angular acceleration α and the moment of inertia or moment of inertia J of the decoupled components depends. The moment of inertia or mass moment of inertia J of the uncoupled components does not change over the lifetime of the components and can therefore be stored in the control unit as a constant.

Since the decoupled components move during their deceleration through a speed band, the speed measurement is advantageously carried out several times at different speed reference points or in different speed ranges, so that the angular acceleration and the drag torque for several different, measured at a time interval speeds can be determined. As a result, the plausibility or accuracy of the determined angular acceleration and the calculated drag torque can be improved.

Preferably, the drag torque is calculated according to the relationship MS = J x α + MBkonst - MAkonst, where J is the moment of inertia or moment of inertia and α is the angular acceleration of the rotating components, and where MBkonst is a constant accelerating moment and MAkonst is a constant decelerating torque. If MAkonst and MBkonst are known, there is a linear relationship between the determined angular acceleration and the drag torque calculated from it. If MAkonst and MBkonst are constant, they can be determined on the test bench and stored in the control unit. If the two moments are not completely constant, the variable proportions can be adapted.

According to a further preferred embodiment of the invention takes place in the subsequent connection of the four-wheel drive, the precontrol of the torque and thus the acceleration of the decoupled components on the basis of the calculated drag torque to provide a comfort optimal jerk-free transition from two-wheel drive in the four-wheel drive. In other words, during active acceleration of the decoupled components, the torque applied for acceleration is precontrolled as a function of the calculated drag torque. Since the drag torque of the secondary axis is also temperature-dependent because of the temperature dependence of the viscosity of the lubricating oil in the axle drive, where neither a temperature sensor is to be installed nor in the control unit a model of the change in the drag torque depending on the temperature is stored, the calculated drag torque only then used for feedforward control of the torque in the subsequent connection of the four-wheel drive, when the measurement of the rotational speeds or the calculation of the drag torque on the one hand and the connection of the four-wheel drive On the other hand, they are close together in terms of time. In this case, it can be assumed that the temperature between the measurement and the precontrol has not changed or only insignificantly changed.

If the influence of the lubricating oil temperature on the drag torque is known and according to a model of the change in the drag torque depending on the lubricating oil temperature stored in the control unit, according to a further advantageous embodiment of the invention, a wear-related or wear-compensated portion of the drag torque can be calculated by the from the moment of inertia or mass moment of inertia and the angular acceleration calculated drag torque is compared with a stored in the control unit reference drag torque, which was determined at the same temperature on the test bench. Where no temperature sensor is to be installed, the drag torque at the beginning of a drive cycle can be determined for this purpose, since the lubricating oil temperature and the temperature of the rotating components at this time correspond to the ambient temperature, assuming a sufficiently long service life. The ambient temperature is normally measured in motor vehicles and is therefore known so that it can be used by the control unit.

If, according to a further advantageous embodiment of the invention, a model of the change in the drag torque as a function of the temperature is stored, the instantaneous lubricating oil temperature in the axle drive of the secondary axle can be calculated or at least estimated on the basis of the calculated wear-related or wear-compensated drag torque component.

• Fig. 1 zeigt eine schematische Darstellung eines Antriebsstrangs eines Kraftfahrzeugs mit einem abschaltbaren Allradantrieb, bei dem die Hinterachse zu- und abschaltbar ist;
• Fig. 2 zeigt den zeitlichen Verlauf der Drehzahl einer Verbindungswelle des Antriebsstrangs nach dem Öffnen einer Allradkupplung und einer Trennkupplung im Antriebsstrang;
• Fig. 3 zeigt eine schematische Darstellung eines Antriebsstrangs eines anderen Kraftfahrzeugs mit einem abschaltbaren Allradantrieb, bei dem die Vorderachse zu- und abschaltbar ist.

In the following the invention will be explained in more detail with reference to an embodiment shown in the drawing.

• Fig. 1 shows a schematic representation of a drive train of a motor vehicle with a disengageable four-wheel drive, in which the rear axle is switched on and off;
• Fig. 2 shows the time course of the rotational speed of a connecting shaft of the drive train after opening an all-wheel drive clutch and a clutch in the drive train;
• Fig. 3 shows a schematic representation of a powertrain of another motor vehicle with a disengageable four-wheel drive, in which the front axle is switched on and off.

This in Fig. 1 An illustrated output of the transmission 4 is connected to a permanently driven primary axle 5 of the motor vehicle 1, which is the front axle. Another output of the transmission 4 is connected via an all-wheel drive 6 with a switchable secondary axis 7, which is the rear axle. When the all-wheel drive clutch 6 is open, the torque of the internal combustion engine 3 is completely applied to the primary axle 5. When the four-wheel clutch 6 is closed, the torque of the internal combustion engine 3 is distributed both to the primary axis 5 and to the secondary axis 7.

The secondary axle 7 comprises an axle drive 8 with a differential compensation 9, which is connected by a connecting shaft 10 in the form of a propeller shaft to the output side of the four-wheel drive 6, two side drive shafts 11 which are connected to the wheels 12 of the secondary axle 7 and the differential compensation 9, as well a four-wheel clutch 13. The four-wheel clutch 6 and the clutch 13 are opened and closed by a control unit 14 of the motor vehicle 1 to separate the connecting shaft 10 and the axle 8 together with differential compensation 9 for switching off the four-wheel drive from the gear 4 and the side hinge shafts 11 and when connecting the four-wheel drive to the transmission 4 and the side hinge shafts 11 to connect.

When the four-wheel drive 6 is a friction or multi-plate clutch with two running in an oil bath disk sets 15, 16, of which the disk set 15 rotatably connected to an output shaft 17 of the transmission 4 and the disk set 16 rotatably connected to the connecting shaft 10. The separating clutch 13 is designed as a dog clutch and comprises a switching element 18, which is connected by a control line 19 to the control unit 14. A speed sensor 20, which measures the speed of a differential cage 22 of the differential compensation 9 and transmits it to the control unit 14 via a signal line 21, is mounted on the axle drive 8.

The switching on and off of the four-wheel drive is carried out by the control unit 14 as a function of the respective driving situation. The shutdown of the four-wheel drive serves the purpose of achieving consumption savings by minimizing the drag torque of the transaxle 8 of the secondary axle 7 when the four-wheel drive is not needed.

When switching off the four-wheel drive, the closed four-wheel drive 6 and the closed clutch 13 are opened at time t1, as in Fig. 2 indicated by the two curves A and B. Once the four-wheel clutch 6 is fully released and the clutch 13 is fully disengaged, as in Fig. 2 Shown at time t2, the connecting shaft 10 are decoupled with the disk sets 16 of the four-wheel drive 6 and the axle 8 with the differential compensation 9 and their rotating components on the one hand by the transmission 4 and the other side of the side drive shafts 11 of the secondary axis 7 and rotate freely. As a result of the drag torque acting on the uncoupled components 8, 9, 10, 16, the rotational speed n of the connecting shaft 10 then gradually decreases to zero, as in FIG Fig. 2 indicated by the curve C.

With the speed n of the connecting shaft 10, the speed n of the differential carrier 22 of the differential compensation 9 decreases, which is measured by the speed sensor 20 in short time intervals .DELTA.t and transmitted through the signal line 21 to the control unit 14.

wobei ω die Winkelgeschwindigkeit der abgekoppelten Bauteile 10, 16, 22, 23 und

die erste Ableitung der Winkelgeschwindigkeit ω über der Zeit t oder der Gradient der Winkelgeschwindigkeit ω ist.From the transmitted speeds n and the time intervals At in the control unit 14, the negative angular acceleration α or deceleration of the differential carrier 22 and thus also the connecting shaft 10 and the other decoupled components, such. B. the disk sets 16 and a drive train 23 in the axle 8, calculated according to the following relationship: $$\mathrm{\alpha }=\frac{\mathrm{dw}}{\mathrm{dt}}=\underset{,}{\overset{.}{\mathrm{\omega }}}$$

where ω the angular velocity of the decoupled components 10, 16, 22, 23 and

is the first derivative of angular velocity ω over time t or the gradient of angular velocity ω.

If the calculated angular acceleration α exceeds a predetermined test value determined after a short debounce time, which depends on the speed and longitudinal acceleration of the motor vehicle 1 at time t1, indicating that the decoupled components 10, 16, 22, 23 are faster than expected can be slowed down, it can be concluded that there is a defect, which is likely to be a bearing defect in one of the pivot bearing of the connecting shaft 10.

wobei MAkonst ein konstanter abbremsender Momentenanteil, MBkonst ein konstanter beschleunigender Momentenanteil und J das Trägheitsmoment oder Massenträgheitsmoment der abgekoppelten Bauteile 10, 16, 22, 23 ist.In addition, the calculated angular acceleration α after the debounce time is related to a drag torque MS of the secondary axis as follows: $$\mathrm{\alpha }=\frac{\mathrm{MS}+\mathrm{MAkonst}+\mathrm{MBkonst}}{\mathrm{J}}$$

where MAkonst is a constant decelerating torque component, MBkonst is a constant accelerating torque component and J is the moment of inertia or mass moment of inertia of the decoupled components 10, 16, 22, 23.

MAkonst and MBkonst are determined in test bench tests and stored in the control unit 14. The moment of inertia or mass moment of inertia J of the decoupled components 10, 16, 22, 23 is known and is likewise stored in the control unit 14.

Thus, in the control unit 14, the drag torque MS of the secondary axis 7 can be determined according to the following relationship: $$\mathrm{MS}=\left(\mathrm{J}\times \mathrm{\alpha }\right)+\mathrm{MBkonst}-\mathrm{MAkonst}$$

The drag torque MS determined by the control unit 14 can be used to optimize the precontrol of the torques applied by the internal combustion engine 3 at the next activation of the four-wheel drive. If neither a temperature sensor installed in the axle 8 still in the control unit 14, a model of the dependence of the drag torque MS is deposited by the oil temperature in the axle 8, but because of this dependence, the time between the measurement of the inflowing into the calculation of the drag torque MS speeds n and the Shifting the four-wheel drive should not be too long to exclude intermediate temperature changes.

If the influence of the oil temperature in the axle transmission 8 on the drag torque MS known by previous test bench tests and the temperature dependence of the drag torque MS is stored in the control unit 14, statements can be made about a wear-related or wear-compensated portion of the drag torque MS beyond. For this purpose, the measurement of the Speed n and the determination of the angular acceleration α and the calculation of the drag torque MS at the beginning of a drive cycle, as long as the temperature of the decoupled components 10, 16, 22, 23 and the lubricating oil in the axle 8 still correspond to the ambient temperature and thus the oil temperature is known. The calculated drag torque MS is then compared with a reference drag torque MSRef determined by test bench tests for the same temperature and stored in the control unit 14. If the calculated drag torque MS exceeds the stored drag torque MSRef by a certain amount, this amount corresponds to the wear-related portion of the drag torque MS.

If the wear-related portion of the drag torque does not change with temperature and the dependence of the non-wear-related portion of the drag torque MS is deposited by the oil temperature in the axle 8 in the controller 14, the wear-related portion of the drag torque MS can be used again to provide information about the to make instantaneous oil temperature in the axle 8.

This in Fig. 3 schematically illustrated motor vehicle 1 differs from the motor vehicle in Fig. 1 in that the permanently driven primary axle 5 is the rear axle and the secondary axle which can be engaged via the four-wheel drive coupling 6 is the front axle 7 of the motor vehicle 1. The differential compensation 9 is formed there as an axle differential and separated from the axle 8. Corresponding parts as in Fig. 1 are denoted by the same reference numerals. As described above, the rotational speed of one of the decoupled components 10, 16, 22, 23 is also measured at a time interval and an angular acceleration α of the decoupled components 10, 16, 22, 23 is determined therefrom. The other method steps described above are the same.

Claims (8)

1. Method for operating a vehicle (1) comprising an all-wheel drive that can be enabled and disabled and a drive train (2) which comprises two clutches (6, 13) actuated by a control unit (14) for enabling and disabling the all-wheel drive and components (10, 16, 22, 23) rotating between the two clutches (6,13), the components being driven when the all-wheel drive is enabled and are uncoupled from the remaining drive train (2) when the all-wheel drive is disabled, wherein when the all-wheel drive is disabled, the rotational speed (n) of at least one of the uncoupled components (10, 16, 22, 23) is measured in a time interval, characterised in that from the measured rotational speed an angular acceleration (a) of the uncoupled components (10, 16, 22, 23) is determined, wherein a drag torque (DT) is calculated on the basis of the determined angular acceleration (a) and a moment of inertia or mass moment of inertia (J) of the uncoupled components (10, 16, 22, 23).
2. Method according to claim 1, characterised in that a defect is indicated when the determined angular acceleration (a) fails to meet or exceeds a predetermined critical threshold value.
3. Method according to claim 1, characterised in that the drag torque (DT) is calculated for a plurality of different rotational speeds (n) measured in the time interval.
4. Method according to any of the preceding claims, characterised in that the drag torque (DT) is calculated according to the relationship $$\mathrm{DT}=\mathrm{J}\times \mathrm{\alpha }+\mathrm{DecTconst}-\mathrm{AccTconst}$$

   

   where J is the moment of inertia or mass moment of inertia and α is the angular acceleration of the uncoupled components (10, 16, 22, 23), where DecTconst is a constant decelerating torque, and AccTconst is a constant accelerating torque.
5. Method according to any of the preceding claims, characterised in that the torque for acceleration is pilot-controlled as a function of the calculated drag torque (DT) upon the next active acceleration of the uncoupled components (10, 16, 22, 23).
6. Method according to claim 5, characterised in that the pilot control of the torque for accelerating the uncoupled components (10, 16, 22, 23) is only carried out as a function of the calculated drag torque (DT) when the time period between the measurements of the rotational speed (n) of at least one of the uncoupled components (10, 16, 22, 23) and the engagement of the all-wheel drive is less than a predetermined time period.
7. Method according to any of the preceding claims, characterised in that the calculated drag torque (DT) is compared with a stored reference drag torque (DTref) and from the latter a conclusion is drawn about a wear-induced or wear-compensated component of the drag torque (DT).
8. Method according to claim 7, characterised in that a current oil temperature is determined in an axle drive (8) from the wear-compensated component of the drag torque (DT).

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